PURPOSE: To improve the strength of a partition wall for composing a device, prevent heating of the device, and reduce energy consumption.

CONSTITUTION: A partition wall 1 is provided with thin wall parts 14, 14... formed thereon while a floating body 3 is provided with targets 15, 15.... The thin wall parts 14 are provided with notches formed on the outer circumferential surface 1a of the partition wall 1 in its longitudinal direction and are located in positions opposite to magnets 10 and 11. Since the thickness of the partition wall 1 is formed large except for the thin wall parts 14, the strength of the partition wall 1 is enhanced, and since the magnetic force of the magnets 10 and 11 act on the targets 15 through the thin wall parts 14, the floating body 3 can be supported by a small amount of exciting current.